Solar Heated Seed Starting

Report From An Opinionated Gardener – May 10

In my sermon last Sunday I mentioned starting seeds in our solar-heated shed. This brief remark drew more after-church questions than the rest of the service combined. “Could I use my shed to grow things?” one woman asked. My answer was, “It depends.”

The shed my husband built is around 18 feet long and 14 feet wide, and the peak of the roof runs east to west. This means that one of the long, sloped sides faces south, and one north. The shed is divided in half down the center, and the side that faces north is used to store tools. The side that faces south is where the seeds are started.

The roof that faces south has cellular, double walled, polycarbonate panels in it. There are also small windows on the upright wall. This side of the shed is insulated, floor, walls and ceiling, which plays an important part in keeping solar heat inside.

A happy accident helps hold that heat. I wanted a place to store my many clay pots, so my husband built shelf units on the inside center wall of the south side and all the pots were stacked there. They act as a heat sink because the sun shines on them all day and they retain and release that warmth later. Yes, there are more effective ways to create a heat sink, but this functions well for us in a number of ways so nothing else is needed.

Data loggers that we’ve had in the shed for three years show that after mid-February the nighttime low temperatures don’t go below 35 degrees. Starting in March, the temperatures stay above 40 so that I can begin starting seeds toward the end of March. Perennial seeds that require a chilling period can be planted in flats outside in January and brought into this shed in March.

On sunny days from mid-April on we need prop open the door on the western side, and open the eastern window to allow for some of the heat to escape. Starting in mid-may we often open the south-side windows and the door to the tool area as well. When the shed is closed up around 4 PM there is still plenty of heat in the pots to keep the area warm all night.

Do I still want a heated greenhouse? Of course! I’d love to have a good place for our orchids and tropical plants, not to mention a spot for winter rejuvenation. But I’m well equipped and grateful for the type of seed starting that we do in the spring.

The interior has just enough space to move around - and this will soon be filled with some of the larger tomatoes and dahlias, which we put on the floor.

There are a few holly trees on the western side of the shed but these don't shade it much.

What a wonderful shed! I just got a small potting shed built last fall but it is on the north side of the tractor shed so it will not serve for seed starting. But I should think about getting more use out of our unheated Great Room which faces south. Hmmmmmm. Thanks for the nudge.